Plays inside your own copy of Valheim, on your device, not in a browser tab. Opens github.com in a new tab.
How to play
Have your own copy of Valheim installed: the mashup plays inside it.
Download it from its release page on GitHub (it runs on Windows).
Install it as its page says. What it asks for is just below, in the list's words.
Start the game the way its page says: some mashups come with a launcher of their own.
What it asks for
Valheim on Steam, an owned Minecraft: Java Edition account, and roughly 3 GB of additional RAM for the Minecraft guest. The creator documents Gale/r2modman-style mod-manager setup and an optional guided installer.